1. Field of the Invention
The present invention relates to an electrofusion polyethylene pipe joint and, more particularly, to a rapidly deployable pipeline system for containing and transporting low pressure fluids.
2. Description of the Prior Art
With the advent of modern day warfare and terrorist activities, there exists a need for a system which may be rapidly deployed and activated to create obstacles delaying and obstructing advancement of armed personnel and armored vehicles, such as tanks. One such system has been proposed which employs plastic pipe wound in long lengths on large spools or reels, such that the pipe may be unwound from the reel and deployed in the ground by a trencher. The lengths are fused together at their ends to form a continuous length of underground pipe which may run over, for instance, several hundred meters. The deployed pipeline may then be filled with a high energy fluid, such as nitromethane, to be held in the ready for detonation at an opportune time to explode and excavate a trench which may be on the order of ten feet deep and twenty feet wide thus instantaneously creating an obstacle to advancement of armored vehicles. The advantages of such a system are recognized in that the pipeline may be laid along a course defined by, for instance, the perimeter of an airstrip, sensitive headquarters or even an international border. Such methods of deployment are characterized by certain drawbacks. First, the overall size of the spools necessary to spool large diameter plastic pipe, on the order of six inches in diameter, without subjecting the pipe to a permanent set or collapsing the wall thereof, results in unwieldly equipment difficult to transport and readily detectable in the deployment area. Additionally, rapid deployment of such a line over long distances multitude of spools thus raising the difficulty of transporting such spools and spooling equipment to and from the deployment site and spacing thereof along the course of the pipeline to be laid.
Thus, the advantages attendant assembly of such a pipeline utilizing multiple lengths of pipe, on the order of 20 or 30 feet per length, have long been recognized. Such pipe lengths could be easily bundled together for air transport and parachuted into the area of deployment. Such pipe lengths, being relatively light, could be deployed along the intended course of the pipeline by ground personnel and subsequently coupled together at the site. However, the realization of a practical pipeline system of this type has been long in coming since mechanical joints have proven expensive and impractical and typical fusion joints require on the order of 15 to 20 minutes to complete in the field thus rendering installation under combat conditions impractical. Consequently, there exists a need for an electrofusion joint which may be rapidly assembled and fused in the field.
Numerous different electrical fusion joints have been proposed in the past. A number of such electrofusion joints incorporate heating sleeves telescoped in coaxial relationship between a female connector and the male pipe. A joint of this type is shown in U.S. Pat. No. 3,378,672 to Blumenkranz. Joints of this type, while satisfactory for their intended use, suffer the shortcoming that they require three pieces, male connector, female connector and sleeve, to make a joint and typically incorporate low power heating coils. Thus, the field personnel would be faced with the necessity of transporting and assembling a separate sleeve at the site with the formation of the joint requiring on the order of 15 to 20 minutes at the best, all under tense conditions which contribute to the likelihood of error or incomplete fusion.
Other electrofusion joints have been proposed which incorporate a tubular body telescopable over the ends of plastic pipes and receiving a thermoplastic sleeve telescoped within the interior thereof. The heating coils are then gradually heated to about 180 degrees centigrade or 356 degrees Fahrenheit. A device of this type is shown in U.S. Pat. No. 4,362,684 to Thalmann. Again, such a joint suffers the shortcoming of requiring, in addition to the pipes being joined, two extra pieces. Furthermore, it has been common practice to heat such coils relatively gradually with about 20 amperes of power, thus requiring on the order of 15 to 20 minutes to achieve fusion.
Other efforts have led to electrofusion joints incorporating a bell connector for telescopical receipt of the end of an adjoining pipe, with a reinforcement tube being telescoped into the interior of the end of such pipe and a heating coil sleeve received coaxially between the pipe and bell fitting. This construction requires the application of an external compression force to compress the bell onto the heating coil during the fusion process. A device of this type is shown in U.S. Pat. No. 3,788,928 to Wise. While satisfactory for applications where time is not of the essence, such devices suffer the shortcoming of requiring multiple components and the application of external compressive forces during the fusion process.
U.S. Pat. No. 4,508,368 is another example of a bell connection joint incorporating a low temperature heating coil which requires external compression during the fusion process.